Ring interferometer with an arrangement to eliminate false indications

Abstract

A ring interferometer which has a light waveguide with two ends which act as the two separate coupling points so that light from a source can be coupled into each of the ends to travel in the light waveguide to be uncoupled from the opposite end as an output beams characterized by the source of light emitting light pulses whose duration is smaller than the transit time of the light in the light waveguide and whose time interval between pulses is greater than the transit time.

I claim: 
     
       1. In a ring interferometer having a light source, at least one light sensitive surface of a detector, a light waveguide which is wound in the coil and has two ends, each end providing a separate coupling point at which light from the coherent source is coupled into the light waveguide and propagates to the opposite end for output coupling therefrom as output beams, said interferometer including means for receiving the output beams and directing portions thereof in a superimposed fashion to the light receiving surface, the improvements comprising means for reducing adulterating influences of undesirable interference light from reflected and back-scattered light components, said means for reducing including said light source being a pulsed light source producing a sequence of individual light pulses having a pulse duration (t) and an interval of time (T) between two consecutive light pulses, said pulse duration (t), said interval of time (T) and a predetermined length of the light waveguide between the coupling points being matched to one another so that the pulse duration (t) is smaller than the length of travel time required by the light to pass over the predetermined length of the light waveguide and the interval of time (T) between pulses is greater than said length of travel time, and said means for reducing including means for gating out a majority of the undesirable interference light at each detector. 
     
     
       2. In a ring interferometer according to claim 1, wherein the predetermined length corresponds to the overall length of the light waveguide. 
     
     
       3. In a ring interferometer according to claim 1, wherein said means for gating out includes a gate circuit being triggered by a pulse from said light source so that the gate circuit is closed except to a point in time just prior to the detector receiving the superimposed output beam. 
     
     
       4. An interferometer, comprising: a loop of fiber optic material;   means for introducing a first light pulse and a second light pulse into said loop, said first and second light pulses having opposite directions of travel in said loop so that said first and second light pulses overlap in a predetermined segment of said loop;   means for combining said first and second light pulses to form an interference pattern; and   means for monitoring the interference pattern, said monitoring means being responsive to backscattered waves which originate only in said predetermined segment.